Differential Readout for Optical Fingerprint Detection

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Solution Overview

Problem

Fingerprint detection in display panels, such as touch screens, faces challenges due to weak current signals and noise interference from parasitic capacitance and bias voltage jitter, making accurate signal detection difficult.

Innovation Solution

Implementing a differential read-out architecture with a display panel comprising multiple photosensitive circuits and switches, where one circuit generates a reference signal and another generates a detection signal, allowing for noise cancellation without the need for a shielding layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If optical fingerprint detection is implemented using photo detectors in the display panel, then fingerprint recognition capability is improved, but noise interference from parasitic capacitance and bias voltage jitter deteriorates signal detection accuracy

Engineering Contradiction:

Improvefingerprint recognition capabilityVSAvoidsignal detection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The photo detectors are divided into two groups: first photo detectors that generate reference signals and second photo detectors that generate detection signals. This segmentation allows the system to separate noise components from actual fingerprint signals, improving measurement precision while maintaining fingerprint recognition capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A detection circuit is introduced as an intermediary component that processes signals from both photo detector groups. This circuit performs differential amplification to cancel out noise from parasitic capacitance and bias voltage jitter, thereby improving signal detection accuracy without compromising the fingerprint recognition function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If shielding layers are added to reduce noise interference, then signal detection accuracy is improved, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improvesignal detection accuracyVSAvoidstructure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention extracts and eliminates the need for shielding layers by using a different approach - dividing photo detectors into two groups and using differential signal processing. This removes the harmful factor (noise) through circuit architecture rather than physical shielding, reducing device complexity while maintaining signal detection accuracy.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention replaces the mechanical/physical shielding layer approach with an electrical/circuit-based solution. By using differential amplification in the detection circuit, the system achieves noise cancellation without requiring additional physical shielding structures, thereby reducing device complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If additional shielding layers are added to reduce noise, then signal detection accuracy is improved, but manufacturing cost increases

Engineering Contradiction:

Improvesignal detection accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention uses standard detection circuits and photo detectors that are already part of the display panel structure, rather than requiring expensive additional shielding materials. The solution leverages existing components arranged in a specific configuration, making manufacturing more cost-effective.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enhances the accuracy of fingerprint detection by canceling noise and eliminating the need for additional shielding layers, thereby improving overall performance without increasing costs.

Implementation Method 1

the first photosensitive circuit is configured to accumulate first charges in response to first incident light to generate a first signal, and the second photosensitive circuit is configured to accumulate second charges in response to second incident light to generate a second signal

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11222933B2Display panel equipped with function of detecting an object, and method for detecting an object on a display panel

Publication Date: 2022.01.11 HIMAX TECH LTD

AI summary

A display panel equipped with function of detecting an object and an associated method are provided. The display panel includes a first photosensitive circuit, a second photosensitive circuit, a detection circuit, a first switch and a second switch. The first photosensitive circuit and the second photosensitive circuit accumulate first charges and second charges in response to first incident light and second incident light to generate a first signal and a second signal, respectively, wherein the object reflects light emitted from the display panel to generate the second incident light. The detection circuit discharges the first charges for converting the first signal into a reference signal on a first input terminal of the detection circuit, and the second signal is transmitted to a second input terminal of the detection circuit, to make the detection circuit to generate a detection signal indicating a difference between the second signal and the reference signal.